1. Field of the Invention
The present invention relates to port collars for use in a tubular string. Specifically, the invention relates to a two-position port collar which can be repeatedly opened and closed and securely retained in each position.
2. Background of the Related Art
Port collars typically have a tubular housing which can be made up into a tubular string to form a part thereof. The port collar has a sliding sleeve disposed therein which may be used to selectively communicate fluid flow between an annular area of the well and an interior of the tubing string. In one example, a port collar is installed in a tubular string in a closed position and the tubular string is then inserted into a wellbore, locating the port collar at a predetermined depth in the well. Packing elements are installed above and below the port collar to isolate a specific zone of the annulus. Thereafter, the sliding sleeve of the port collar is remotely opened and the interior of the tubular is placed into communication with production fluid in the annulus. The port collar may also be used to permit fluid flow from the interior of the tubing string into the annulus of a well. For example, in cementing deep wells, a two-part cementing job is often used wherein the lower portion of a casing or liner string is cemented and then, using a port collar, the upper annulus is cemented to avoid hydrostatic pressures present in the lower portion of the annulus.
While many port collar designs have been made and used, certain problems exist with current designs. For example, most port collars rely on shear screws or some other type of mechanically shearable connection to unlock the sleeve from an initial position and permit movement of the sleeve to a second position within the collar. In a typical example, the shearable connection holds the sleeve in a closed position and then, when the collar is in the wellbore and ready to be opened, the shearable members are caused to fail with mechanical or hydraulic force. Once the shearable connection has failed, the sleeve is left prone to accidental shifting in the housing, unless it is permanently locked into either an open or closed position.
There is a need therefore, for a port collar that does not rely on a shearable connection to lock the sleeve into position within the housing. There is a further need for a port collar that can be repeatedly shifted and locked into the opened and closed positions. There is yet a further need for an easily shiftable port collar that can be used with other port collars in a single tubular string to create a larger assembly for selectively exposing different areas of an annulus to communication with the interior of the tubing string.
The present invention generally provides a port collar assembly comprising a housing and a sleeve disposed therein. The sleeve is moveable between a first or opened and a second or closed position relative to the housing. In the closed position, the port collar prevents communication of the fluid between the exterior and interior of the port collar. The assembly includes a locking system for each position comprising ratchet teeth formed on the exterior surface of the sleeve and mating ratchet teeth formed on the interior surface of the housing. One set of mating ratchet teeth are designed to secure the sleeve in an opened position within the housing and a second set of mating ratchet teeth secures the sleeve in a closed position. In one aspect of the invention, the ratchet teeth on the interior surface of the housing are formed on the inner surface of an inwardly biased C-ring disposed in a groove formed in the interior surface of the housing. A plurality of buttons are disposed within apertures formed in the exterior surface of the sleeve and the buttons can be urged in an outward radial direction by a shifting tool disposed within the sleeve. The buttons urge the C-rings into the grooves of the housing and out of engagement with the mating ratchet teeth formed on the surface of the sleeve. In this manner, the sleeve and housing are unlocked from each other and the tool can be shifted to the other position.
In another aspect of the invention, cavities and shifting shoulders are formed on the interior of the sleeve opposite each locking system. Corresponding unlocking and detenting formations are formed on a shifting tool including a formation designed to urge the buttons of the sleeve in a radial outward direction. A shifting surface on the shifting tool, corresponding to a shoulder formed on the interior of the sleeve, allows a force to be applied to move the sleeve to a second location in the housing after being unlocked.
In another aspect of the invention, several port collars are installed in a tubular string in a wellbore. Thereafter, in order to open and close the port collars, a number of shifting tools are run into the well on a run-in string in a pre-determined, spaced-apart orientation. The shifting tool at the lowest point on the string opens each port collar as it passes therethrough. In order to close the port collars, the string of shifting tools is pulled upwards and the shifting tool designed to close the port collars closes each collar as it passes therethrough. By accurately spacing the shifting tools along the run-in string, the direction of the string can be reversed in order to open a certain port collar while leaving the others in a closed position.